Former Jewish school students and religious leaders have expressed "deep concern" about references to "homosexual cure" group JONAH in a JFS Jewish studies lesson, and have called for schools urgently to address the teaching of homosexuality.

Former JFS head girl Alma Smith has written to the school's headmaster, Jonathan Miller, saying that not making reference to lesbian and gay organisations in a Jewish studies lesson was "as good as saying that JONAH is a good idea, even if those words aren't used."

Ms Smith asked JFS to invite Keshet UK, the Jewish Lesbian Gay Bisexual and Transgender forum, to run seminars in school and teacher training. Keshet has recently been added to UJIA's roster of speakers on Jewish subjects whom it sends to mainstream schools. Last week Keshet ran a session at Highgate School on being young, Jewish and gay.

Dalia Fleming, who left JFS in 2007, also wrote to Mr Miller, saying that she had experienced similar, controversial JS classes on homosexuality. "During that class we were told that if you happened to be gay, it would be better that we spoke to a rabbi and members of our community to help us. I had to defend my sexuality, identity and my religious beliefs to the entire class."

But Mr Miller wrote to parents this week claiming that the JC's story was "simply wrong." He maintained that "students were not shown a website from JONAH", and said that "JFS did not, and would not teach, [that] homosexuality can be cured." The school, he said, "explicitly teaches that Orthodox Judaism entirely condemns homophobia and discrimination of any kind."

The Rabbinic Conference of Liberal Judaism said in a statement: "What is clear from all the different versions [of the lesson procedure] is that JONAH was mentioned as an option, meant to give students 'food for thought'. What was presented was a dangerous point of view that advocates unsafe medical practices, unsupported by science and unsupportable by all those of good conscience."